Re: How to make this exception-safe

From:

Martin Bonner <martinfrompi@yahoo.co.uk>

Newsgroups:

comp.lang.c++.moderated

Date:

Wed, 19 Nov 2008 15:27:29 CST

Message-ID:

<11cc04fd-cdc5-4606-8743-7639927571c8@k1g2000prb.googlegroups.com>

On Nov 18, 6:43 pm, Triple-DES <DenPlettf...@gmail.com> wrote:

Consider the following code:

#include <vector>

struct C {
   explicit C(int) {} // may throw
   private:
     C(const C&);
     C& operator=(const C&);

};

struct V {
   V() {
     // may leak if push_back or C::C(int) throws
      v_.push_back( new C(2) );
      v_.push_back( new C(1) );
      v_.push_back( new C(3) );
   }

   ~V() {} // delete all elems of v

private:
   std::vector<C*> v_;

};

How would you go about making an exception-safe version of V::V()?
This is what I could come up with:

// 1st attempt
#include <memory>

V::V() {
   v_.reserve(3);

   std::auto_ptr<C> c1( new C(2) );
   std::auto_ptr<C> c2( new C(1) );
   std::auto_ptr<C> c3( new C(3) );

   v_.push_back( c1.release() );
   v_.push_back( c2.release() );
   v_.push_back( c3.release() );

}

Which is tedious if you are inserting more objects. Does anyone have a
better solution?
PS! boost/tr1 shared_ptr or similar can not be used.

    V::cleanup()
    {
      while (v_.size() > 0) { delete v_.back(); v_.pop_back(); }
    }

    V() {
        try {
          v_.push_back( new C(2) );
          v_.push_back( new C(1) );
          v_.push_back( new C(3) );
        } catch (...) {
          cleanup();
          throw;
        }
    }

(you can then use cleanup from the destructor too).

If your management have a problem with boost, then a clone of
shared_ptr is probably the best solution though. (Why can't you use
it?)

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